Electronic devices containing active organic materials are attracting increasing attention for use in devices such as organic light emitting diodes (OLEDs), organic photoresponsive devices (in particular organic photovoltaic devices and organic photosensors), organic transistors and memory array devices. Devices containing active organic materials offer benefits such as low weight, low power consumption and flexibility. Moreover, use of soluble organic materials allows use of solution processing in device manufacture, for example inkjet printing or spin-coating.
An OLED comprises an anode, a cathode and one or more organic light-emitting layers between the anode and cathode. Non-emissive layers, for example charge transporting layers, may be provided between the anode and cathode.
Suitable light-emitting materials include small molecule, polymeric and dendrimeric materials. Suitable light-emitting polymers include poly(arylene vinylenes) such as poly(p-phenylene vinylenes) and polyarylenes such as polyfluorenes.
Holes are injected into the device through the anode and electrons are injected through the cathode during operation of the device. Holes in the highest occupied molecular orbital (HOMO) and electrons in the lowest unoccupied molecular orbital (LUMO) of a light-emitting material combine to form an exciton that releases its energy as light.
Theoretically, 25% of excitons are singlet excitons, that can emit light from a singlet excited state, the remaining 75% of excitons being triplet excitons. Radiative decay from a triplet excited state is formally forbidden, however emission from a triplet excited state by spin-orbit coupling using heavy transition metal complexes is known. However, typically phosphorescent materials are rare metals, for example, iridium or platinum complexes. Blue phosphorescent emission remains a problem.
Thermally activated delayed fluorescence (TADF) is disclosed in the Japanese Journal of Applied Physics 53, 060101 (2014).
It is an object of the invention is to provide efficient organic light-emitting materials and devices.
It is a further object of the invention to provide efficient organic blue light-emitting materials and devices.